Brain activity and function have been shown to oscillate at particular frequencies. These may encode feedback and feedforward processes across different cortical regions and layers. Recently, several studies have found oscillations to also exist in reaction time rates during attentional cuing tasks in the alpha (7-12Hz) and theta (4-8Hz) ranges. Because of convergence with neurophysiological findings and the use of cuing paradigms, these oscillations have been linked to attentional sampling of visual information. We wanted to investigate whether similar patterns in behavior could be observed in perceptual shape processing not explicitly linked to attention. We conducted a series of psychophysical experiments in which subjects saw a fat/thin Kanizsa square stimulus, followed by a local mask, and, after a variable delay (SOA), either a local or a global mask (Ringach & Shapely, 1996). We observed oscillations in performance in a masking paradigm that used no explicit attentional cues. The SOA was titrated in steps of 16.7 ms between 0 and 533 ms. Discrimination accuracy fluctuated by up to ±10% as a function of SOA in the alpha and theta ranges for both local and global mask conditions. Oscillation amplitude was somewhat larger for locally masked stimuli. A control experiment using a 2AFC version of the task showed that these fluctuations were perceptual in nature, and not due to fluctuations in response criterion. We also found that confidence fluctuated with accuracy, indicating that observers were aware when a stimulus was more or less visible. We hypothesize that behavioral oscillations may mirror neural oscillations and may reflect feedback and feedforward signaling in perceptual processes such as contour completion and masking, and are not solely signals of attentional sampling.